Many drains and sewers (hereinafter generally termed drains) were constructed many years ago and the wall structures are now badly eroded or collapsing. In order to repair such damage, it has been proposed to insert a liner within the drain to provide a new water-impervious wall to the drain. However, the wall of the drain is often not continuous since branch drains debouch into the main drain through an entry port in the wall of the main drain. Where a liner is installed, it is necessary to cut an aperture in the liner wall in register with this entry port to allow the free flow of fluid from the branch drain into the main drain.
It has been proposed to locate the entry points for the branch drains by visual survey of the drain before the liner is installed and then to cut the apertures after the liner has been installed by running a suitable cutting machine along the drain for the required distance. However, since most liners are opaque or metallic, the accurate register of the cutting tool with the actual entry port of the branch cannot be achieved visually and dead reckoning measurement has to suffice.
The branch drain often enters the main drain at an angle so that the axis of the branch is not normal to the axis of the main drain. This further complicates the accurate registry of the cutting tool with the actual entry port of the branch drain.
I have now devised a method and apparatus which reduces the above problems.